Climatic cooling, Major glaciation, Sea level drop are the following possible causes for the Ordovician-Silurian extinction.
Option: A, B, D
Explanation:
In geological time scale Ordovician and Silurian are the epoch of Mesozoic era. Others are Devonian, Carboniferous and Permian. Almost 300-400 B.C. ago these periods were in work. Each of the epoch and period has their own characteristics regarding plant and animal life like Carboniferous was famous for the formation of coal.
There is a some sorts of natural reason for the extinction or discontinuation of each period and introduction of new period in geological time scale. Major glaciations mean accumulation or solidification of snow at large scale due to extreme cooling which causes reduction of sea level height.
